1. Field of the Invention
The present invention relates to a small-sized high reliability semiconductor device, a manufacturing method thereof and a semiconductor module which uses the same.
2. Description of the Related Art
Recently, along with rapidly growing demands for mobile communication apparatus, power amplifiers for them have become a target of energetic research and development activities. To meet the needs for smaller communication apparatus, monolithic microwave integrated circuits (MMICs), which are small semiconductor chips with built-in passive components, are incorporated in power amplifier modules. In these ICs, heterojunction bipolar transistors (HBTs) are mainly used since they allow high power densities and miniaturization. Note that hereinafter in the present specification, monolithic microwave integrated circuits and heterojunction bipolar transistors are abbreviated as MMICs and HBTs. respectively.
In particular, in miniaturization-oriented power amplifier modules, MMICs are mounted face up on ceramic substrates by using metal bumps. Typical examples of this technique are disclosed in, for example, Japanese Patent Laid-Open No. 1994-204449 (Patent Document 1) and Japanese Patent Laid-Open No. 2001-2106677 (Patent Document 2).                <Patent Document 1> Japanese Patent Laid-Open No. 1994-204449        <Patent Document 2> Japanese Patent Laid-Open No. 2001-2106677        
From a practical point of view, let us review the structures of HBT-used conventional semiconductor modules and make their problems clear. Firstly, consider a face-down configuration in which a semiconductor device having electrodes, wirings and passive components as well as active components formed on the semiconductor substrate is electrically connected to the module substrate by using what are called bumps and made of a thick conductor layer. This configuration has a structural problem that the conductor layers required to connect the components and electrical members to the module substrate differ in thickness namely due to the different thicknesses of the components and electrical members. Accordingly, it is difficult to secure the mechanical strength of the MMIC itself. This causes some difficulties in reliability. In addition, since semiconductor substrate is connected to the MMIC side via bumps, electrical contact points must be formed peripherally. Resistances are introduced in proportion to the number of such contact points. These many electrical contact points are disadvantageous in terms of durability, too.
Prior art structures have a problem in terms of usability, too. For example, if a semiconductor substrate is mounted face up on an MMIC substrate via bumps, other components such as passive elememts can not be formed on the back side of the semiconductor substrate before bumps are formed thereon. Therefore, it is not possible to form wiring lines, etc. on the back side of the semiconductor substrate. In addition, if no bump is formed below the active component, that is, all bumps are formed on the back side of the semiconductor substrate only to connect components to the module substrate, thermal radiation from the active component in the MMIC to the back side of the semiconductor substrate may not be satisfactory, resulting in unstable operation of the active component.